Complexity levels of electronic device testing vary tremendously, from simple manual low-volume/low-complexity testing performed with perhaps an oscilloscope and voltmeter, to personal computer-based medium-scale testing, to large-scale/high-complexity automated test equipment (ATE). Manual and personal computer-based testing are typically applied when testing discrete devices, specific components of an integrated circuit, or portions of a printed circuit board. In contrast, ATE testing is used to test functionality of a plurality of complex integrated circuits (ICs) such as memory circuits or hundreds of dice on a wafer prior to sawing and packaging.
When testing ICs on a wafer, it is cost effective to test as many devices as possible in parallel, thus reducing the test time per wafer. Test system controllers have evolved to increase the total number of channels and hence the number of devices that can be tested in parallel. However, a test system controller with an increased number of test channels is typically a significant cost factor for a test system, as is a probe card with complex routing lines used to accommodate multiple parallel test channels. Thus, an overall probe card architecture that allows increased test parallelism without requiring increased test system controller channels and without increased probe card routing complexity and cost is desirable.
FIG. 1 shows a block diagram of an automated test system 100 of the prior art. The test system 100 includes a test system controller 101, a test head 105, and a test prober 107. The test system controller 101 is frequently a microprocessor-based computer and is electrically connected to the test head 105 by a communication cable 103. The test prober 107 includes a stage 109 on which a semiconductor wafer 111 may be mounted and a probe card 113 for testing devices under test (DUTs) on the semiconductor wafer 111. The stage 109 is movable to contact the wafer 111 with a plurality of test probes 115 on the probe card 113. The probe card 113 communicates with the test head 105 through a plurality of channel communications cables 117.
In operation, the test system controller 101 generates test data which are transmitted through the communication cable 103 to the test head 105. The test head in turn transmits the test data to the probe card 113 through the plurality of communications cables 117. The probe card then uses these data to probe DUTs (not shown explicitly) on the wafer 111 through the plurality of test probes 115. Test results are then provided from the DUTs on the wafer 111 back through the probe card 113 to the test head 105 for transmission back to the test system controller 101. Once testing is completed and known good dice are identified, the wafer 111 is diced.
Test data provided from the test system controller 101 are divided into individual test channels provided through the communications cable 103 and separated in the test head 105 so that each channel is carried to a separate one of the plurality of test probes 115. Channels from the test head 105 are linked by the channel communications cables 117 to the probe card 113. The probe card 113 then links each channel to a separate one of the plurality of test probes 115.
With reference to FIG. 2, an ATE switching apparatus 200 of the prior art uses a mechanical relay 201 to switch signals feeding a DUT 207 between a high voltage, low frequency driver 203 (frequently referred to as VHH) and a high frequency, low voltage driver 205 (frequently called the pin driver). The mechanical relay 201 is chosen to switch the signals as relays inherently have both low resistance and low capacitance values. Low capacitance values of the mechanical relay 201 allow high frequency signals to be routed to the DUT 207. Further, the mechanical relay 201 allows high voltage signals to pass to the DUT 207 are well. Voltages as high as about 13 volts are frequently encountered in ATE testing. A plurality of the mechanical relays 201 may be mounted on the probe card 113 (FIG. 1). However, mechanical relays suffer from several inherent problems including physical size, high current consumption, reliability, and switching speed.
Therefore, what is needed is a simple, economical, and robust means of switching both high voltage/low frequency and low voltage/high frequency electrical signals between a probe card and a DUT. Ideally, switching speeds should be high with a low current draw. Further, the switch should also function bidirectionally to allow resulting data from the DUT to be transferred through the probe card to the system controller.